Motor gasoline fuel when stored for a prolonged period of time eventually deteriorates due to oxidation and polymerization. Cracked streams, increasingly being used in gasoline fuel, are worsening the problem. The deterioration of fuel is evidenced by the formation of gums and darkening of color. The gum formation in the fuel system further leads to filter blockage resulting in reduction in fuel flow to the engine.
In general, the process of fuel degradation is very complex in view of the variety of hydrocarbons involved in it. It involves free radical reactions, which are characterized by three distinct stages, viz. initiation, propagation and termination. These reactions are very complex and have implications on the quality of fuel.
Unsaturated compounds such as olefins and dienes contribute to instability by auto-oxidation and/or polymerization reactions in the presence of oxygen. Higher levels of unsaturated compounds in the fuels are due to increased severity of secondary refining operations in Fluid Catalytic Cracking (FCC) as well as renewed blending of streams from thermal processes such as Viscosity Breaker (VB) and Coker. These products are used for blending gasoline fuel in order to meet the growing demand.
Furthermore, only olefins and dienes are not responsible for instability of fuels. In deeply hydrotreated or reformed fuels, most of the natural antioxidants get removed during the process leading to poor stability of the product. If even trace amount of copper is present in the fuel, it shall accelerate the rapid formation of peroxides. The peroxides thus formed shall attack the copper parts of fuel system with the result copper dissolution takes place leading to even more peroxide formation resulting into accelerated oxidation of fuel. Frequent sources of copper contamination are copper-containing alloys in refinery equipment, product distribution systems, chemicals used in the refining and the fuel system of vehicles. The catalytic effect of copper is so strong that even the most effective antioxidants/stabilizers cannot provide adequate stability in the presence of copper, thus resulting in deterioration of the product.
The options available to refiners for improving gasoline fuel quality are limited. The following four main approaches are usually practiced at refineries the world over for improving gasoline fuel quality: selective blending of refinery streams; use of chemical additives; adopting an appropriate processing route, which may include, aromatic extraction, hydrogenation and hydro-cracking; and use of chemical additives in combination with processing.
Aromatic extraction and hydro-cracking options result in significant changes in product yield, whereas hydrogenation has only marginal impact on product balances. The problem of gasoline stability can effectively be solved by the incorporation of carefully selected chemical additives in proper concentrations. These chemical additives primarily retard the natural degradation of gasoline fuel during long-term storage.
Alkyl or aryl substituted hindered phenols are commonly used for stabilization of gasoline fuel. The stearic hindrance in the hindered phenols is provided by bulky substituents in ortho position to the hydroxyl group in the ring of the phenolic antioxidant. These bulky substituents influence the specificity of these phenols by blocking phenoxyl radicals from abstracting hydrogen atoms from organic substrates. 2,6-Di-t-butylphenol (DTBP) is a most widely used functional group in commercial hindered phenolic antioxidants. DTBP is effective and easily made at moderate cost by ortho alkylation of phenol by olefins using ortho selective catalyst. Preparation of nitroalkane based hindered phenols and their antioxidant properties are reported in British Patent No. 1,561,311.
European Patent No. EP 106,799 assigned to Sandoz GmbH describes a mixture of sterically hindered phenols having recrystalisation temperature <10 deg. C. These types of compounds are reported to be useful antioxidants for liquid fuels, especially for gasoline. Canadian Patent CA 1,216,308 assigned to Ethyl Corporation reported p-alkylenes hindered phenols as useful antioxidants for gasoline, lubrication oils, plastics, rubbers etc. U.S. Pat. No. 4,981,495 reported that the oxidation stability of gasoline mixture is improved by adding to the gasoline 1-10,000 ppm of an alkyl-1,2-dihydroquinoline compound, dimer, trimer or polymers. Optionally, a hindered phenol may be jointly used with the quinoline compounds. Halon and Vincent have reported in European Patent EP 427,456 that a liquid mixture of alkyl phenols composed of 2-t-butylphenol and 2,6-di-t-butylpheno are suitable for use as stabilizers for middle distillate fuels, fuel oils etc. European Patent EP 410,577 discusses polymeric reaction products of an ortho substituted phenol as an antioxidant for liquid hydrocarbons such as kerosene and gasoline. German Patent No. 2,917,927 describes that alkylated dihydroxbiphenyls are useful as antioxidants and can help in improving the induction period. Japanese Patent No. 81,92,235 reported trialkyl-tris(3,5-dialkyl-4 hydroxybenzyl)benzene as a stabilizer for rubbers, gasoline etc. However, the disadvantage associated with using a phenolic antioxidant alone includes high treat levels, inability to effectively control peroxides formed during the oxidation process and inability to check retard colour degradation of fuels.
Aromatic amines have been well known as antioxidants but the mechanism of their action has not been well established, as compared to phenolic antioxidants. Basically, some of the aromatic amines are quite complex compositions and a number of oxidation products are obtained from the reaction of aromatic amines and fuel degradation products. Aromatic amines commonly being used are phenylenediamines and diarylamines. However, several synergistic combinations are also documented in the literature.
U.S. Pat. No. 4,279,621 reported that heavy polyamines distillation residues can be used as antioxidants for gasolines at a treat level of 0.05 wt %. Japanese Patent Jpn Kokai Tokyo Koho JP 58,76,492 assigned to Sumitomo Chemical Co. Ltd. reported a mixture of a 2-tert-butyl alkyl phenol, bis (nonyl phenol) amine and ditridecylthiodipropionate as an antioxidant for gasoline, kerosene, light oils and heavy oils. U.S. Pat. No. 4,456,541 assigned to Ethyl Corporation reports that the addition of 3,5-diethyltolune-2,4-diamine or 3,5-diethyltolune-2,6-diamine or their mixture in appropriate concentration provides antioxidant properties to polymers, gasoline, lube oils and other organic compounds.
U.S. Pat. No. 4,871,374 assigned to Petrolite Corp. reported that a fuel oil can be stabilized with an imine-enamine condensate. This additive is claimed to be effective in improving the colour stability and sedimentation of distillate oils. U.S. Pat. No. 4,647,290 reports that the colour deterioration of a distillate fuel oil is inhibited by addition of a mixture of N-(2-aminoethyl) piperazine and HONEt2. A straight-run gasoline fuel containing 200 ppm of N-(2-aminoethyl) piperazine and 300 ppm of HONEt2 was placed in an oven at 140 deg. F. for 14 days, cooled, and filtered; the ASTM colour of the filtrate was 2.5 (ASTM D-1500), compared with 5.0 for the gasoline fuel containing only N-(2-aminoethyl) piperazine. U.S. Pat. No. 5,197,996 reports that a boron based additive helps in the colour stabilization of distillate fuel oil. U.S. Pat. No. 5,035,719 describes that storage stability of middle distillate fuels is improved by adding an acrylate polymer containing moieties derived from 4-vinylpyridine or the enamine ester of morpholine etc. and propionaldehyde as additive. U.S. Pat. No. 4,978,366 reports that distillate fuel especially which has a high acid number initially or which develops a high acid number as a result of fuel degradation, is stabilized with a diaminomethane. Henry and West have reported in U.S. Pat. No. 5,011,504 that block copolymers of acrylic and acrylic amines can be used as additives for fuel oils to diminish sediment and colour formulation. A suitable additive as reported by them is 2-ethylexylmethacrylate-dimethylaminoethyl methacrylate copolymer. U.S. Pat. No. 5,057,123 describes that diesel fuel at high temperature can be stabilized with an amine-containing copolymer selected from aminopropyl morpholine ethylene-propylene-hexadiene copolymer as N-phenylenediamine ethylene-propylene-hexadiene copolymer and N-aminopropyl-N-phenylenediamine ethylene-propylene-hexadiene copolymer. Though amine based antioxidants are excellent oxidation inhibitors for gasoline and other middle distillate fuels, they are costly and their use in fuels adversely affects the economics of oil refineries.
Commercial Cashew Nut Shell Liquid (also known as CNSL) is obtained by hydrogenation of naturally occurring, biodegradable, vegetable based cashew nut shell liquid. CNSL is a reddish brown viscous liquid which occurs in the soft honeycomb structure of the shell of cashew nut. CNSL, extracted from shells with low boiling petroleum either, contains about 90% anacardic acid and about 10% cardol. CNSL, on distillation, gives pale yellow phenolic derivatives which are a mixture of biodegradable unsaturated m-alkylphenols, including cardanol. Catalytic hydrogenation of these phenols produces a white waxy material, predominantly rich in tetrahydroanacardol, which is also known as hydrogenated CNSL. CNSL and its derivatives have been known for producing high temperature phenolic resins and friction elements, as exemplified in U.S. Pat. Nos. 4,395,498 and 5,218,038. Friction lining production from CNSL is also reported in U.S. Pat. No. 5,433,774. Likewise, it is also known to form different types of friction materials, mainly for use in brake lining system of automobiles and coating resins from CNSL.
Mannich condensation products are rarely reported as antioxidants for gasoline. However, they are known to act as dispersants and detergents in various types of hydrocarbon stocks. Their use in lighter hydrocarbon stocks, such as gasolines, has been disclosed in U.S. Pat. Nos. 3,269,810 and 3,649,229. 3,235,484 (Now U.S. Pat. No. Re. 26,330) describes the addition of certain disclosed compositions to refinery hydrocarbon fuel stocks for the purpose of inhibiting the accumulation of carbonaceous deposits in refinery cracking units.
Several distinct disadvantages are associated with using phenolic antioxidants alone. Such disadvantages include high treat levels, inability to effectively control peroxides formed during the oxidation process and inability to stop colour degradation of fuels.
The disadvantage associated with using amine based antioxidants alone is the considerable cost of such compounds, which affects refinery economics, and their tendency to impart colour to gasoline, as some of the amine based antioxidants are quite dark in colour.
The disadvantage associated with using Mannich bases is their poor antioxidant efficacy for gasoline fuel, when used singularly.
Therefore, an object of this invention is to propose a new gasoline antioxidant composition which obviates the above referred disadvantages.
Another object of this invention is to propose a new gasoline antioxidant composition which can effectively control the gum formation during storage and use.
A further object of this invention is to propose a new gasoline antioxidant composition which can effectively control the colour degradation of gasoline.
A still further object of this invention is to propose a new gasoline antioxidant composition with improved antioxidant characteristics.
Another object of this invention is to propose a new gasoline antioxidant composition which when used in gasoline can reduce copper corrosion and pitting tendency up to the desired level.
Yet further object of this invention is to propose a new gasoline antioxidant composition which when used in fuels can help in controlling water emulsification up to the desired extent.
Another object of the invention is to propose a new gasoline antioxidant composition which does not require use of costly metal deactivator in wide variety of gasoline fuel